Effects of interactions between transient granular flows and macroscopically rough beds and their implications for bulk flow dynamics

Steep-creek beds are macroscopically rough. This roughness causes channelised flow material to decelerate and dissipate energy, which are accounted for by depth-averaged mobility models (DMM). However, practical DMM implementations do not explicitly account for grain-scale basal interactions which influence macroscopic flow dynamics. In this study, we model flows using physical tests with smooth and macroscopically rough bases, and hence evaluate Discrete Element Method (DEM) and DMM models. A scaling effect is identified relating to roughened beds: increasing the number of grains per unit depth tends to suppress dispersion, such that small-scale flows on smooth beds resemble large-scale flows on roughened beds, at least in terms of bulk density. Furthermore, the DEM shows that rougher beds reduce the peak bulk density by up to 15% compared to a smooth bed. Rough beds increase the vertical momentum transfer tenfold, compared to smooth ones. The DMM cannot account for density change or vertical momentum, so DMM flow depths are underestimated by 90% at the flow front and 20% in the body. The Voellmy model implicitly captures internal energy dissipation for flows on rough beds. The parameter ξ can allow velocity reductions due to rough beds observed in the DEM to be captured.

Effect of buried depth on thermal performance of a vertical U-tube underground heat exchanger

Many researchers numerically investigated U-tube underground heat exchanger using a two-dimensional simplified pipe. However, a simplified model results in large errors compared to the data from construction sites. This research is carried out using a three-dimensional full-size model. A model validation is conducted by comparing with experimental data in summer. This article investigates the effects of fluid velocity and buried depth on the heat exchange rate in a vertical U-tube underground heat exchanger based on fluid–structure coupled simulations. Compared with the results at a flow rate of 0.4 m/s, the results of this research show that the heat transfer per buried depth at 1.0 m/s increases by 123.34%. With the increase of the buried depth from 80 to 140 m, the heat transfer per unit depth decreases by 9.72%.

A Study of Temperature Distribution and Thermal Stresses in a Hot Rock Due to Rapid Cooling

Thermal stresses may be induced in a hot dry rock when a cold fluid is injected in the well. To study this problem, we look at the thermoelastic response of a hot rock that is suddenly cooled. The cooling is assumed to be either at a constant temperature or at a constant heat flux per unit depth. Our approach is to nondimensionalize the equations and perform a parametric study and look at the temperature distribution and the induced-thermal stresses. The results indicate that depending on the extent of cooling and the cooling time, thermal stresses can be induced. Numerical simulations on sandstone, with an initial uniform temperature of 473 K, are also carried out. The results show that if the cooling is due to the surface temperature maintained at 463 K (10 °C lower than the initial temperature of the hot rock), thermal stresses that are larger than the rock tensile strength could be induced. When the cooling is due to a constant surface heat flux, this temperature can be reached after about 777 days of cooling with a minimum value of a heat flux of −20 W/m.

Corn Emergence and Yield Response to Row-unit Depth and Downforce for Varying Field Conditions

Optimum row-crop planter seeding depth performance is required to place seeds within proper soil conditions to ensure quick germination and maximize the likelihood of uniform emergence. Seeding depth is adjusted prior to planting by selecting a row-unit depth, followed by the adjustment of a row-unit downforce for proper seed-soil contact. Optimum row-unit depth and downforce settings required to maintain a consistent seeding depth are variable. The objective of this study was to evaluate corn ( L) emergence and yield response to row-unit depth and downforce in changing field conditions between sites and growing seasons. Corn was planted with a 6-row John Deere MaxEmerge Plus planter equipped with heavy duty downforce springs. The experiment was conducted in 2014 and 2015 in Central Alabama for non-irrigated corn. Two fields, three row-unit depths (4.4, 7.0, and 9.5 cm), and three row-unit downforce settings (0.0, 1.1, and 1.8 kN) were evaluated. Emergence was measured at 75 and 100 Growing Degree Days (GDDs). Yield was measured using a yield monitor installed on the combine harvester. Corn emergence was mainly affected by changes in weather conditions. Row-unit depth and downforce did not affect corn emergence in warmer weather conditions but the 4.4 cm row-unit depth resulted in more emergence than the other row-unit depth settings in cooler weather conditions. Yield ranged from 8,000 to 13,000 kg ha-1 across treatments and yield was mostly affected by changing growing conditions between fields and growing seasons. Plant population significantly varied with treatments, but lower plant populations did not always result in lower corn yields. These findings provided a better understanding of corn emergence and yield response to row-unit depth and downforce in varying field conditions. Keywords: Corn, Depth, Downforce, Emergence, Maize, Planter, Yield.